Enhanced Dechlorination of Carbon Tetrachloride by Immobilized Fulvic Acids on Alumina Particles

Fulvic acids (FA) were immobilized on alumina particles in order to evaluate their catalytic effect as solid-phase redox mediator (RM) during the reductive dechlorination of carbon tetrachloride (CT) by anaerobic sludge. FA were extracted from three different soil samples and two commercial composts. Electron carrying capacity (ECC) was determined in all FA samples in order to select the appropriate source of redox-mediating compounds for CT dechlorination. TiO₂, Al(OH)₃, and γ-Al₂O₃ particles were tested as immobilizing materials for the extracted FA. FA extracted from a temperate pine forest soil showed the highest ECC (291.72 μmol g⁻¹). The highest adsorption capacity of FA, measured as total organic carbon (TOC), was achieved by alumina (γ-Al₂O₃) particles (12 mg TOC-FA g⁻¹). Results suggest that the transfer of electrons rather than their microbial generation through glucose fermentation was the rate-limiting factor during dechlorination of CT. Immobilized FA increase up to 10.4-fold the rate of CT dechlorination as compared with the control lacking FA. Immobilization of FA on alumina particles was very stable, and spectrophotometric screening did not detect any detachment of FA during dechlorination of CT, thus confirming that the enhanced dechlorination achieved could exclusively be linked to the redox-mediating capacity of immobilized FA. The present study constitutes the first demonstration that immobilized FA on alumina particles could serve as a solid-phase RM in dechlorination reactions.